The continuous casting of metal, especially steel, is now on an industrial scale and makes it possible to cast not only bars, often called billets, but also slabs, i.e., metal sheets of substantial width which, for example, can exceed 2 meters.
In general terms, a continuous-casting installation comprises, in the casting direction, a tundish intended for receiving the liquid metal coming from the steel plant in ladles, a bottomless mold and a device for extraction and secondary cooling.
The tundish serves to ensure casting continuity, especially when a ladle which is finished casting is replaced. The bottomless mold located underneath the tundish and supplied continuously from the latter consists of two parallel longitudinal walls and two transverse walls mounted on a frame and limiting a casting cavity of rectangular cross-section for the casting of slabs, the large sides being formed by the longitudinal walls and the small sides by the transverse walls. The walls of the mold are limited inwards by a plate in contact with the metal, usually made of copper and also called a "friction plate". At least the longitudinal walls are equipped with a cooling system which normally consists of channels for the circulation of a liquid coolant, usually water, along the inner face of the contact plate. Consequently, there forms along the cooled contact plates a solidified skin, the thickness of which increases progressively downwards and within which the liquid metal is retained, thus making it possible to extract via the bottom of the mold a strand of metal, the cross-section of which corresponds to that of the mold. To prevent the metal from adhering to the contact plates, the mold is usually subjected to a slight oscillating movement which can be generated by various well-known mechanisms.
The strand of metal issuing from the bottom of the mold then passes into a secondary cooling device which generally consists of a series of guide elements forming a corridor arranged in the extension of the mold and of the same cross-section as the latter, each guide element being equipped with means of retaining and cooling the strand of metal. On the other hand, to make it easier to extract the strand of metal, at least some guide elements are equipped with means which exert a pull on the strand.
Continuous-casting machines originally worked only in a vertical direction, then curved casting machines were produced, and in these the secondary cooling device aligns the strand of metal horizontally, so that the latter can easily be cut into slabs capable of subsequently being rolled in the conventional way.
The known machines possess means of adjusting the dimensions of the cast product, in particular by shifting the longitudinal walls to adjust the thickness of the strand and the transverse walls to adjust its width. However, the possibilities of adjustment remain limited, since each machine is intended for casting products of a certain category. There is, nevertheless, a provision for casting several bars of small width at the same time from a machine designed for casting slabs, the cavity of the mold being divided longitudinally by means of transverse partitions spaced apart from one another, so as to form several cavities placed next to one another and each having a thickness corresponding to the distance between the longitudinal walls. For various reasons, in the known machines, this thickness has to remain relatively substantial, for example at least 100 mm. Consequently, known continuous-casting machines have not to date been used for the continuous casting of strips.
For this purpose, various systems have already been proposed. For example, in French Pat. No. 69 45 157, the metal is introduced from the bottom upwards between two cooled cylinders forming the two walls of the mold in which the strip forms, the latter remaining laid against one of the cylinders until it solidifies. Such systems present many problems and have not been successful on an industrial scale.
To avoid the disadvantages which the development of machines of a new type entails, the subject of the invention is a new arrangement making it possible to produce thin strips on a machine of the conventional type described above, the mode of operation of which is consequently well known.